Does 'hvis'' not mean ''if'' ?
It can also mean "if", yes
How do you know when its ´if´ instead of ´whose´ ( are there any rules or is it a ¨you´ll figure it out as you go along¨ type of thing?)
'If' is a conjunction while 'whose' is a pronoun. They are used in pretty different ways, so it's hard to mix them up.
EDIT: "Whose" is a possessive adjective. (Oct '19)
Why can't this be, "whose tour is it?"
It would be an appropriate translation. You can use tur to talk about the tour of some musician, for instance.
Note that "tour" is not a good translation of tur in the general case. The Danish tur usually refers to a relatively short trip.